Young Star Animations 2014
We're looking at the spatial positions of the members of known nearby young moving groups - the circles are the galactic plane at 25 and 100 parsecs (the lines point to the galactic center and galactic north pole). These moving groups range from well-studied ones like Ursa Major, beta Pictoris, and TW Hydra, to less well known ones like Octans and Carina. What makes these groups particularly difficult to study is that they're incredibly spread out- they cover large regions of space, overlap with each other, and some are all over the sky. You can't simply point a telescope at one region and expect to get all, or even most of the members. These groups are extremely sparse- if you compare them to a sample of all stars within 25 parsecs (even one that's not yet volume-complete; the RECONS 25 pc list has ~2100 star systems where we expect ~6000), you'll notice how thinly spread these groups are. The nearest neighbors of members of the group are not other members of the group.
This movie shows the UVW spatial VELOCITIES (relative to the Sun) of all the nearby stars that someone has considered as a member of a nearby young moving group. This is in velocity space, so objects that are moving in parallel through space -- regardless of where they are -- should appear as a single point, and co-moving groups of stars should appear as clusterings.
The box (from Zuckerman & Song 2004) is where all stars less than 150 Myrs old are supposed to exist, and I can see about four clusters in there. If I turn on the colors, you can see which cluster is which. One is the beta Pictoris moving group, one is AB Doradus, one is Tuc-Hor, and the rest are smushed up into the fourth one. Now, I'm not saying those groups aren't real, I'm just saying you can't identify them with kinematics alone, you need more information. Prior to Hipparcos and its high precision astrometry, everything within the box was blurred together and it was called the "Local Association". After Gaia and its vastly improved precision, we may be able to break these groups up further.